1. Field of the Invention
The present invention relates to a magnetic one-component toner for use in image forming apparatuses, such as copying machines, printers and facsimiles, employing electrophotography method, electrostatic storage method, or the like.
2. Description of Related Art
Generally in image forming methods such as electrophotography method and electrostatic storage method, the surface of a photosensitive material is charged by corona discharge or the like, and then exposed by laser or the like to form an electrostatic latent image. This electrostatic latent image is then developed with a toner to form a toner image. This toner image is then transferred to a storage medium to obtain a high quality image. This image forming method often employs a powdered magnetic one-component toner, which can be obtained by adding a coloring agent, charge control agent, release agent, magnetic powder, etc. to a binding resin composed of a thermoplastic resin, etc., followed by kneading, grinding and classification.
To achieve high quality image, the above magnetic one-component toner calls for miniaturization of particle size. However, there arises the problem that the miniaturization of particle size deteriorates toner flowability. As a method of solving this problem, Japanese Patent Application Publication Laid-Open Nos. 2-236566, 2-157027, and 2-300763 disclose methods of adding an additive, and describe the conditions under which the additive is blended with a toner, and the form of the additive. Unfortunately, such a method of adding an additive is insufficient to improve the flowability of the miniaturized toner. Hence, an improved method is demanded.
On the other hand, Japanese Patent Application Publication Laid-Open No. 5-289398 discloses a method in which the volume average particle size of toner is set to a specific value, and compressibility is adjusted to not more than 30%. However, there arises the problem that when the compressibility is too small, a toner layer on a sleeve is apt to be nonuniform, making it difficult to achieve a uniform image.
Japanese Patent Application Publication Laid-Open No. 2000-29239 discloses a method in which the mean roundness of a toner manufactured by grinding process is adjusted to a specific value. This toner seems to have higher transfer efficiency. For this reason, when this toner is used in a developing apparatus provided with a developing sleeve of high charge applying force, the toner in the vicinity of the surface of the developing sleeve has an extremely high charge and, under reflection force it is strongly attracted to the sleeve surface, resulting in an immobile layer. This decreases the chance that the toner is rubbed with the sleeve, thereby inhibiting the charge application. As a result, due to nonuniform charge of the toner, a toner thin layer formed on the developing sleeve causes turbulence and lack of uniformity to deteriorate image quality.
Japanese Patent Application Publication Laid-Open No. 2002-91142 discloses a developing apparatus construction and a method of adjusting the particles size, flowability, and compressibility of a toner to a specific value. However, because this toner is ground by a jet stream grinder, its mean roundness is low. When this toner is miniaturized, its flowability is lowered, which can cause the toner density drop.